Autonomous monitoring method and system using sensors of different sensitivities

ABSTRACT

A method and system of monitoring for chemical or other toxic agents includes operating a plurality of first type sensors having a first level of sensitivity to an agent in a monitored area. Concurrently a second type sensor is operated having a second level of sensitivity to the agent in the monitored area, where the second level of sensitivity is at least ten times more sensitive than the first level of sensitivity. Input from the plurality of first type sensors and the second type sensor is received and analyzed, at a central location, in order to determine the presence of the agent in the monitored area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e)to provisional application No. 60/564,233 filed on Apr. 22, 2004, thedisclosure of which is incorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to a method and system formonitoring an area for chemical or other toxic agents using autonomoussensors having different sensitivities.

BACKGROUND OF THE INVENTION

A growing risk of asymmetric attacks has increased the need fordistributed chemical detectors or detectors for other agents with vastlysuperior false positive rates relative to current solutions. Using twotiered sensors for detecting biological or other hazards are known.However, these known arrangement of two tiered sensors typically consistof two types of sensors that are co-located at a sensor location suchthat the more sensitive or more reliable sensor is only operated ortriggered when the less sensitive or less reliable sensor initiallydetects a presence of an agent that is being monitored.

However, in view of the risks posed by terrorism, some of the chemicalwarfare and other toxic agents need to be monitored over a vast area.Use of such known co-located dual sensors may be prohibitively expensiveif used to cover such a vast area that needs to be monitored.

SUMMARY OF THE INVENTION

In certain embodiments, the present invention provides a method ofmonitoring for chemical or other toxic agents, including: operating aplurality of first type sensors having a first level of sensitivity toan agent in a monitored area; concurrently operating a second typesensor having a second level of sensitivity to the agent in themonitored area, wherein the second level of sensitivity is at least tentimes more sensitive than the first level of sensitivity; and receivingand analyzing, at a central location, input from the plurality of firsttype sensors and the second type sensor in order to determine thepresence of the agent in the monitored area.

In certain embodiments, both the plurality of first type sensors and thesecond type sensor are operated continuously.

In certain embodiments, both the first type sensors and the second typesensors are chemiresistor based sensor arrays.

In certain embodiments, the chemiresistor based sensor arrays areconductive polymer composite vapor sensors.

In certain embodiments, a preconcentrator is provided with the secondtype sensor.

In certain embodiments, the present invention provides a system formonitoring for chemical or other toxic agents, including: a plurality offirst type sensors, having a first level of sensitivity to an agent,arranged in a monitored area; a second type sensor, having a secondlevel of sensitivity to the agent, arranged in the monitored area, and acentral analysis unit connected to the plurality of first type sensorsand the second type sensor, wherein the central analysis unit analyzesdata from the plurality of first type sensors and the second type sensorin order to determine the presence of the agent in the monitored area.

In certain embodiments, the present invention provides a method formonitoring for chemical or other toxic agents, including: operating afirst type sensor having a first level of sensitivity to an agent in amonitored area, operating a second type sensor having a second level ofsensitivity to the agent in the monitored area, and receiving andanalyzing, at a central location, input from the first type sensor andthe second type sensor in order to determine the presence of the agentin the monitored area, wherein the first type sensor and the second typesensor each comprise a plurality of orthogonal sensing technologies on asingle sensor array, wherein a transduction mechanism in each of thesensing technologies detects a change in electrical resistance.

In certain embodiments, the present invention provides a system formonitoring for chemical or other toxic agents, including: a first typesensor, having a first level of sensitivity to an agent, arranged in amonitored area; a second type sensor, having a second level ofsensitivity to the agent, arranged in the monitored area, and a centralanalysis unit connected to the first type sensor and the second typesensor, wherein the central analysis unit analyzes data from the firsttype sensor and the second type sensor in order to determine thepresence of the agent in the monitored area, wherein at least one of thefirst type sensor or the second type sensor comprises a plurality oforthogonal sensing technologies in a single sensor array, wherein atransduction mechanism in each of the sensing technologies detects achange in electrical resistance.

In certain other embodiments, the present invention provides a method ofmonitoring for chemical or other toxic agents, comprising: operating aplurality of first type sensors having a first level of specificity to agroup of agents in a monitored area; concurrently operating a secondtype sensor having a second level of specificity to the group of agentsin the monitored area, wherein the second level of specificity is morespecific than the first level of specificity; and receiving andanalyzing, at a central location, input from the plurality of first typesensors and the second type sensor in order to determine the presence ofthe agent in the monitored area.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate a presently preferredembodiment(s) of the invention, and, together with the generaldescription given above and the detailed description given below, serveto explain the principles of the invention.

FIG. 1 is a block diagram illustrating the arrangement of sensors incertain embodiments of the present invention.

FIG. 2 illustrates the change in property of a polymer in the presenceof a vapor.

FIGS. 3 and 4 provide examples of the data obtained for testing ofsensors with HD and GA.

FIG. 5 is a diagram illustrating a tested sensor's response over a rangeof blister (0-5 mg/m³) and nerve agent (0-1 mg/m³) concentrations.

FIG. 6 is a discrimination plot for chemical warfare agents over wideranges in concentration.

FIG. 7 is a diagram that illustrates the detection limit of sensors to awide range of analytes.

FIG. 8 is a graphical display of the time to detect versus concentrationfor specific toxic industrial chemicals.

FIG. 9 is graph illustrating sensor response times versus film thicknessfor polymer composite sensors.

FIG. 10 is diagram illustrating the use of a SWCNT network chemiresistoras a sensor.

FIG. 11 is a diagram that illustrates performance of a sensor arrayconsisting of different types of chemiresistors to different analytevapors.

FIG. 12 is a diagram illustrating a graphical user interface that may bedisplayed at a control station.

FIG. 13 shows a micromachined preconcentrator.

FIG. 14 is graph that illustrates the variation in response of theCASPAR preconcentrator with temperature.

DETAILED DESCRIPTION OF THE INVENTION

The applicants have developed low cost, array based, nanocomposite basedsensor technology based on earlier work at Caltech as described forexample, in U.S. Pat. No. 5,571,401 and its related patents. Thesepatents are incorporated herein for all purposes. This technology hasbeen demonstrated to be sensitive to a wide range of chemicals,environmentally robust, accurate (e.g. not susceptible to falsepositives), low cost, reliable, and easily upgradeable.

In certain embodiments, the present invention provides a distributedmonitoring system based on this technology. This system incorporateshighly distributed low cost, less sensitive nodes (or sensors) able todetect at the Immediately Dangerous to Life or Health (IDLH) level andbelow (as one example of a first level of sensitivity). The system alsoincorporate “truth nodes” that integrate this detection technology withmore sensitive nodes, for example, nodes that include miniaturizedpre-concentrators. These “truth nodes” (or more sensitive nodes) detectat a 10 or 100 times lower level of concentration, for example, than thelow cost, less sensitive nodes but are often more expensive and takelonger to make measurements. The combination of these two detectionapproaches result in the lowest cost and most highly capable system.This system utilizes the information from the two different node typeseither individually or collectively at a central location or at adistributed network of locations that are each centrally located for aset of sensors. In certain embodiments, the system also includes acentral command monitor that allows all of the nodes in the system to bemonitored from one central location. Therefore, for example, each of thedistributed network of locations, or a subset thereof, may communicatewith the one central location so that the entire system may be monitoredfrom the one central location.

FIG. 1 is block diagram that illustrates the arrangement of sensors incertain embodiments of the invention. FIG. 1 is exemplary only and oneskilled in the art would recognize various modifications andalternatives all of which are considered a part of the presentinvention. A plurality of first type sensors 10 are arranged to monitoran area and the monitored area also includes one or more second typesensors 20 (only one shown in FIG. 1). Data from the less sensitive orless specific (and therefore typically lower cost and lower power) firsttype sensors 10 and from the more sensitive (or more specific) secondtype sensor 20 are sent to a central analysis unit 30. It should benoted that the central analysis unit 30 may be located where it directlyreceives data from the first type and second type sensor. Alternatively,the central analysis unit may be located at a central location 50 wheredata from the one or more monitored areas may be transmitted over apublic or private wide area network 40 (which may be the Internet whichis a public wide area network) to the central location. In yet anotheralternative, all the sensors in a monitored area may transmit their datato an “intermediate” central analysis unit 30 with a multitude of suchintermediate central analysis units transmitting the received data to aremote central analysis unit located at the central location 50. Itshould be noted that each of the first type sensors 10, the second typesensors 20, the central analysis unit 30, and the central location 50(with its analysis units) include processors, memory, and program codethat are configured to perform the collection, transmission, andanalysis of sensor data that is discussed further herein.

The communication from the first type sensor 10 and the second typesensor 20 to the central analysis unit 30 may be by a directpoint-to-point communication link as shown by the solid lines in FIG. 1.Alternatively, the first type sensors 10 and the second type sensors 20may communicate with each other in a mesh type communication network sothat the communication originating at one of the sensors reaches thedestination central analysis unit 30 through one or more intermediatenodes or sensors. The dotted lines in FIG. 1 are indicative of thecommunication between the sensors or nodes in such a mesh communicationnetwork which enables an originating sensor or node 10 or 20 tocommunicate with the central analysis unit 30.

The first and second type sensors provide a low cost, low power andhighly sensitive chemical detector capable of continuous distributedmonitoring of both chemical warfare agents (CWAs) and toxic industrialchemicals (TICs) and provides for improved monitoring of buildings andfacilities.

As discussed earlier, applicant has developed low cost, array based,nanocomposite based sensor technology based on earlier work at Caltech.This technology has been demonstrated to be sensitive (IDLH and PELdetection) to a wide range of chemicals, environmentally robust,accurate (e.g. not susceptible to false positives), low cost, reliable,and easily upgradeable. This core technology is reviewed below andresults supporting the performance standards are detailed.

One embodiment of the present invention proposes a distributedmonitoring system based on this technology. This system incorporateshighly distributed low cost nodes (or first type sensors) able to detectat the Immediate Danger to Life or Health (IDLH) level of concentrationand below. The system will also incorporate “truth nodes” (or secondtype sensors) that are more sensitive and detect much lowerconcentrations of the agents of interest. For example, these truth nodesmay integrate this detection technology with miniaturizedpreconcentrators. These “truth nodes” may detect at 10 to 100 timeslower level than the low cost nodes but are typically more expensive andtake longer to make measurements. The combination of these two detectionapproaches result in the lowest cost and most highly capable systempossible.

Most simple, low cost chemical sensors produced today are directed atthe detection of a single compound or class of compounds. Typicalexamples include electrochemical cells, metal oxide semiconductors (socalled Taguchi sensors), pilasters, and photionization detectors. Moresophisticated systems designed to identify multiple chemicals arecomplicated but vacuum systems, complex sampling systems, or expensivedetection schemes. Recently, array based sensors have been demonstratedthat combine the ability to identify a wide range of analytes with thelow cost and simplicity of single compound detectors.

Arrays of conductive polymer composite vapor sensors were developed atCaltech and have been optimized by applicant. In this approach, thepresence of a chemical is detected through a change in the electricalresistance of a chemically sensitive resistor. These sensor films arederived from composites that contain regions of a conducting phase withregions of an insulating organic material. This approach allows use of awide range of polymeric materials with a range of chemical bindingproperties, so that an enormous diversity in array composition can beachieved using readily available conventional polymeric materials. Whena vapor is present, sorption-induced swelling of the polymer produces achange in the electrical resistance of the material due to the swellingof the film. As shown in FIG. 2, when the vapor is removed, the swellingreverses (see 101 and 101′)and the resistance returns to its originalvalue. These responses of these sensors have been proven to be arereversible over tens of thousands of vapor exposures as well asreproducible over a large number of trials under a variety of ambientconditions. With the emergence of newer nanomaterials that can serve asthe conducting phase, even greater chemical diversity and sensitivity isachievable.

To verify the sensitivity of these sensors, live agent testing atBattelle Memorial Institute (BMI) has been completed. Test results forHD, GB, GA, DMMP and phosgene (CG) in air confirm detection of low partsper billion level of agents for a hand held chemical point detector. Inaddition, a high degree of response repeatability and sensor stabilitywas demonstrated even at the lowest limit of detection. An example ofthe data obtained for HD and GA is shown in FIGS. 3 and 4. For thesesensors, discrimination between HD and GA is seen clearly betweensensors 9 and 11 and sensors 10 and 12 at all concentrations tested. Asshown in FIG. 3, the results 301 for the sensors for blister agentdetection is much superior to the results 305 for the nerve agentsensors in the presence of HD (a blister agent). Likewise, as shown inFIG. 4, the results 405 of the nerve agent sensors is much superior tothe results of the blister agent sensors in the presence of GA (a nerveagent). In general, as shown in FIG. 5, these tested sensors display alinear response (see 501 and 510 in FIG. 5) over a wide range of blister(0-10 mg/m³) and nerve agent (0-100 mg/m³) concentrations.

In addition to H and G-series agents, these composite sensors also showremarkable sensitivity to higher vapor pressure (>1 atm) blood andchoking agents, phosgene (CG) and hydrogen cyanide (AC). An example ofthe response measured for 137 ppm phosgene is shown in thediscrimination plots 601 in FIG. 6 where even at this low concentration,the new sensor array can clearly distinguish between all the agentstested, as well as common chemical interferents (toluene, diesel fuel).It is estimated that the detection levels for detection of blood orchoking agents are in the low ppm range.

In certain embodiments, the sensitivities described above can be furtherenhanced by incorporation of a miniaturized preconcentrator. Prior workhas clearly indicated that sensitivities of 100 fold are achievable withminiaturized preconcentrators. This allows for Permissible ExposireLimit (PEL) level detection even in instances where the fundamentalsensing technology cannot achieve this level. Therefore, certainembodiments of the present invention provide for combining simplesensing nodes for IDLH (or less sensitive) detection with moresophisticated nodes that incorporate preconcentrators for PEL (or moresensitive) level detection.

As shown in the diagram 701 of FIG. 7, the detection limit of thesesensors to a wide range of analytes has been measured and is commonly inthe low ppb for CWAs and TICs. While the absolute detection levels ofgases such as hydrogen cyanide and phosgene are higher than those forCWAs, the detection capability is still significantly below immediatelydangerous to life and health (IDLH) levels.

Results for specific TICs (NO₂ 801 and acrylonitrile 810) are presentedin FIG. 8 in the form of time to detect versus concentration curve.Applicant has already developed sensor materials that can detect TICs ofinterest at or below IDLH (803, 812) and PEL (805, 814) levels in wellless than two minutes and further improvements are achievable.

Any sensing system must be able to perform under a wide range ofexternal conditions including wide variation in humidity, temperature,and confounding environments. The live agent testing has includedtesting sensors over a varying temperature and humidity.

Detection on fully autonomous devices was determined as part of avalidation study on five hand held devices with temperature variedbetween 10 and 40° C., humidity between 1-80% relative humidity, andinterfering elements including 1% each of AIFF, diesel fuel, bleach,antifreeze, ammonia, vinegar, floor wax, Windex, and Spray 9 cleaner.These results are summarized below. The results indicated that thedevices were able to detect G series nerve agents at or below the JointServices Operational Requirement (JSOR) requirements (0.1-1.0 mg/m³) andwas able to detect blister agents below JSOR requirements (2 mg/m³).

With respect to temperature, the following results were observed:

-   -   At 0° C., all 5 tested units were operational (function test        only, no agent challenge).    -   At 10° C., all 5 tested units correctly alarmed to GB and HD in        all tests (10/10).    -   At 40° C., all 5 tested units correctly alarmed to GB and HD in        all tests (10/10).

Based on the above results, temperature and humidity are not significantrisks to reliable operation of the sensors used in certain embodimentsof the present invention.

In total, over 300 validation experiments were conducted on 5 differenthand held devices. Overall prediction success for one of these units hasbeen analyzed using receiver operator characteristic (ROC) curves. Theresults of these experiments clearly demonstrated very favorablespecificity (false positive ratio) and sensitivity (false negativeratio).

One of the advantages of sensors provided by the present invention isthat it uses technology characterized by the low cost nature of thesensing materials as well as the read out electronics and the use ofsuch sensors in the two or more tier arrangement discussed hereinwherein a plurality of low cost sensors (of lower sensitivity and/orspecificity) are arranged concurrently with a higher cost sensors (ofhigher sensitivity and/or specificity) so that a large area can becontinuously and effectively monitored for chemical and other toxicagents. This arrangement of low cost sensors is ideally suited for awidely distributed, low cost monitoring system.

This sensing technology has been tested in the industrial market andthis product has demonstrated excellent reliability in the field. Inaddition to this field experience, extensive laboratory testing of thesensor technology itself has been conducted. These tests indicatedlittle sensor degradation, even when challenged with higher thanexpected agent concentrations.

Another element of a successful sensor is that the manufacturing processbe robust with high manufacturing yields. Applicant has developed arobust manufacturing process for polymer composite sensors. The sensoruniformity was recently investigated for the arrays sent for live agenttesting. A comparison of the training data for six units under testdemonstrated a high degree of uniformity across these units.

Another feature of certain embodiments of the present invention is theexpandability of the system. Because the detectors use an array basedapproach and these sensors are broadly sensitive to a wide range ofchemistry, the system can easily be upgraded to detect new threats byupdating the identification algorithms, either on board the device, orthrough a centralized data analysis system. In fact, the commercial handheld device that is sold by applicant is designed to be “user trained”so that the same product is used in a vast array of differentapplications by simple changes to the on-board algorithms. Theinstrument is designed so that these changes can be made by the enduser. In one embodiment, these upgrades are provided to the user viadownloadable software upgrades (if local data analysis is implemented)or in a seamless manner if remote data analysis is implemented.

As discussed earlier herein, certain embodiments of the presentinvention use polymer composite sensors for CWA and TIC detection. Theperformance of these existing materials can be improved through improveddeposition methods and control of film thickness. As shown in the graph901 in FIG. 9, while the response of these sensors is rapid (typicallyless than 30 seconds), the response time is proportional to t², where tis the film thickness. Thus, a reduction of film thickness from 1 micron(for example, the film thickness in certain embodiments) to 500 nmimproves response time by 4 fold and result in response timessignificantly less than ten seconds. Thus, certain embodiments of thepresent invention provides for an improved sensor with a filmthicknesses less than or equal to 500 nm and ideally with a filmthicknesses less than 100 nm.

Additional improvements in the composite sensors can be accomplishedthrough modifying both the non-conducting and conducting phases as apart of investigating materials and optimizing their performance. Thereare indications that some of these materials may have sensitivities thatare 4-10 times better than previously demonstrated.

In certain embodiments, the present invention uses novel fillermaterials that improve sensor sensitivity. Recent work with single wallcarbon nanotubes (SWNTs) has demonstrated a potential for enhancedsensitivity to a wide range of chemicals including nitrogen dioxide andother strong oxidizing or reducing agents. It has also been recentlydemonstrated that certain metal nanoparticle conductors also producesensors with enhanced chemical sensitivity and these sensors are alsoused with certain embodiments of the present invention. Use of SWNTs andSWNT networks is described, for example, in J. P. Novak et al., APPL.PHYS. LETT., vol. 83, 4026 (2003), which is incorporated herein for allpurposes.

In addition to enhanced sensitivity, it is imperative that any newmaterials are also robust to changing environmental conditions. For eachsensor material described above, comprehensive testing of sensitivity,response to humidity, temperature stability, and sensitivity tointerference compounds is performed to test the robustness of the sensormaterials to environmental conditions.

Initial results focused on CW simulant detection clearly indicate thatthese sensors are sensitive to DMMP, a standard nerve agent stimulant,as shown in the graph 1001 in FIG. 10. FIG. 10 also shows an opticalimage 1005 and an AFM image 1010 of a SWNT network chemiresistor and themeasured change in resistance upon exposure to 100 ppb if a chemicalsimulant for nerve agents. The SWNT networks can be patterned with highyield using conventional photolithographic techniques. The use of SWNTnetworks eliminates the need to position individual SWNTs and produces amore easily manufacturable device with a more reproducible response.

To monitor sensor performance, extensive laboratory testing is conductedon the sensor materials. Detection versus response time curves aregenerated and an initial determination of P_(fp) (probability of falsepositives) and P_(fn) (probability of false negatives) are conducted.Some of these arrays are then sent out for live agent testing (at amutually determined surety laboratory) and others are incorporated intothe initial prototypes for system testing. In certain embodiments, thesystem parameters including the analytical models are adjusted so that atarget P_(fa)<0.1% and a target P_(fn)<5% is achieved for all compoundstested at the IDLH level of concentration without preconcentration.

The optimal sensor array uses orthogonal sensing technologies on asingle, simple, platform. Thus, the optimal sensor array includesseveral different chemiresistor approaches, possibly including sensorsin a single sensor array made from regions of conducting andnon-conducting materials, sensors based on intrinsically conductingpolymers (ICPs) and composites made from ICPs, sensors made from singlewall carbon nanotubes (SWNTs) and composites made from SWNTs, metaloxide semiconductor sensors, sensors based on porphyrin materials, andsensors based on metallic nanotubes made from metals and metal oxides.In general, in certain embodiments which use orthogonal sensingtechnologies, each sensor array includes different types of sensors inwhich the transduction mechanism in all sensors measure a change inelectrical properties. Furthermore, in certain embodiments, the at leastone of the sensors has regions of conducting and non conductingmaterial.

FIG. 11 is a diagram that illustrates performance of a single sensorarray consisting of different types of chemiresistors. As illustrated inFIG. 11, such an array made from multiple types of thin filmchemiresistors sensors exhibits a highly differentiated pattern ofresponse to different classes of analyte vapors. Graph 1110 displays theresponse of the PCS polymer composite sensors in the single sensor arrayto DMMP in the air at IDLH concentration level, graph 1120 displays theresponse of SWCNT and ICP conducting polymer sensors in the singlesensor array to presence of ammonia in the air at IDLH concentrationlevel and graph 1130 displays the response of the SWCNT sensors in thesingle sensor array to the presence of HCN in the air at IDLHconcentration level. The use of orthogonal sensing technologies in asingle sensor array provides for greater reliability and range ofdetection by the sensor array.

One of the features of certain embodiments of the present invention isprovision of an electronic platform that provides low noisemeasurements, and appropriate power and communications interfaces. Whilethe detailed design of these components may be refined, a current designis described in more detail in the following paragraphs.

Applicants have determined that current performance is limited byelectronic noise rather than sensor noise. Therefore, there is a focuson improving the electronics design to improve overall signal to noise,and therefore sensitivity, by decreasing the electronic noise. Anelectronic noise reduction of 10× could lead to a 10 fold sensitivityenhancement.

One of the issues in certain embodiments of present invention concernshow to communicate alarms back to a centralized location. There are twocompeting techniques that may make sense depending on installationissues (time, installation cost, etc). One approach is using a powerline carrier. This approach provides a reliability benefit since a wireis used to communicate key information and a cost benefit as it usespre-existing infrastructure to carry this information. The restrictionto this technique is that the sensor must be connected to a power linewhich can add installation cost and/or restrict available deploymentlocations.

The second approach would be a wireless communication protocol. Withimproved mesh networks this approach offers the advantage of being ableto locate a device anywhere (assuming adequate battery power) andreduced installation costs. However, this approach may result in a lessreliable connection in an application where data flow is critical.

The system of this invention is designed to use, among others, wirelessor power line carrier communications and to include a modular approachso that the communications module is a separate part of the sensor node.This allows for a common sensing platform that could be utilized withdifferent communications methods.

With respect to power, the sensor devices can be either battery or linepowered with battery back-up. The advantage of line power is a lowercost of ownership, ability to move away from ultra low power designs,and greater design flexibility of power hungry elements such as thepreconcentrator. The advantage of using battery power is the freedom ofplacement and lower cost of installation (if new power connections arerequired).

In certain embodiments, the system may be designed for distributedmonitoring throughout a building or other location. Therefore, theinformation collected at each sensor can be best utilized if it isbrought back to a central location. Once centralized, this data can befused and further interpretation can be conducted. In addition, theresulting information can be interfaced to control systems and/ordisplayed. This data aggregation and interpretation provides for fewerfalse alarms and centralized information display.

Software is provided that allows each node (for example, the nodes 10 or20 in FIG. 1) to communicate appropriate information back to a centrallocation (for example, the nodes 30 or 50 in FIG. 1). This data caninclude alarm information and raw data for use in further computationsin the central location. The full data transmission can be event driven(e.g. only sent when an event is detected) to minimize band width andreduce complexity. The aggregated data is utilized by the system leveldata interpretation software as described below. Furthermore, as wouldbe recognized by those skilled in the art, the data aggregation could beperformed at several tiers. For example, in one tier, all the data fromall the sensors in one building or location could be aggregated (forexample at node 30) while sensor data from multiple buildings could beaggregated at a second tier (for example, in a central location 50 asshown in FIG. 1).

In certain embodiment, the present invention proposes extensive softwarecontrol for both low level and high-level control of node finction, codeto aggregate and interpret sensor data at a single node, and software toprovide for calibration of devices at the point of manufacture and inthe field. The array based sensing technology discussed herein uses apattern matching approach to detect and identify compounds from alibrary. This library can reside either on the device or at a remotelocation. Applicant's U.S. Pat. No. 6,422,061 provides additionaldetails of detecting and transmitting sensory data and identificationlibraries over a network, the disclosure of which is incorporated byreference herein for all purposes. This approach allows for rapidupgrading of instruments as new threats become important. Analysis oflive agent test data has indicated a 5-10 (or greater) fold improvementin sensitivity and accuracy is achievable through software optimizationat the node.

A network of autonomous sensors reporting to a central location offersthe potential to further reduce false alarms and improve alarmprediction through software deployed at the network level. In certainembodiments, the present invention provides an extensive softwarecapability for sensor data fusion. In one embodiment, one module of thissystem is a symbolic data model that reads discrete data (e.g. alarms,settings) and applies two different mathematical or analyticalapproaches to identify anomalies. In the first case, a set of rules isapplied to this data to generate derived states and anomalies. While themathematical analysis software is generic, the set of rules must bedetermined for a given application so the it may best be described as a“knowledge-based” component. In other words, this portion operates onrules such as: if alarm A sounds do nothing unless alarm B sounds. Inaddition to this rules based module, a second module uses more advancedmathematical tools to identify anomalies. This module utilizes HiddenMarkov Models (HMM) to identify anomalies based on probabilities ofpassing from one state to a second state. The HMM use differentalgorithms to define these probabilities such as a Viterbi algorithm, aforward-backward algorithm, or a Baum-Welsh algorithm, as would be knownto those skilled in the art. All of these methods are designed to findhidden patterns in data. The output is a prediction of an anomaly basedon a number of discrete state variables.

An element of the system provides how information is presented. In oneembodiment, the system of the present invention is an autonomous systemthat interfaces with existing control functions by providing a data feedto these existing control systems. In certain other embodiments. thepresent invention includes other visualization capability such anindication of overall system health with drill down capabilities. Inthis approach, a central display will present a red light/green lightindication (or other similar indicator) of system health/alarm status.On alarm (or system error), further information will be available ingraphical form to indicate the fault/alarm location. This capability mayprove extremely helpful to first responders or other emergencypersonnel. An example of such a GUI 1201 that may be used is shown inFIG. 12.

An element of the system is an understanding of node density anddistribution throughout the facility both from the perspective ofdeploying the nodes and interpreting the results received from thenodes. From the perspective of deploying the nodes in a cost and resulteffective manner, the main principle is that analysis of data fromdiverse networked sensors generates a system whose performance issignificantly better than the sum of its parts. One of the main resultsof applying this principle is the suppression of false alarms frominexpensive generic sensors. This is achieved by using cutting edge dataanalysis with a clustered array of networked sensors (whether of thefirst type sensors and/or second type sensors). At both the array andcluster levels, diverse sensors and optional supplementary sensors suchas meteorological (“met”), GPS, may be used. This allows modeling todesign clustered array configurations to answer a variety of questions,including: whether supplementary sensor are needed with each sensor, oronly with each cluster; what is the optimal distance between sensors andclusters; and what is the effect of weather on specific sensors. Themodeling is also used to answer system-level cross-correlation questionssuch as: what is the best number of sensors per cluster; what is thebest mix of sensor types in a cluster; or is there a combination ofgeneric sensors that can cover for each other's failings, with at leastone type that works in most relevant weather conditions. The data fusionand analysis approach also provides software that can learn patterns ofsystem behavior and optimize its performance at each particular site. Itlearns from its mistakes and evolves to become better using techniquessuch as neural networks which are within the abilities of one skilled inthe art.

From the perspective of interpreting results received from particularnodes, certain embodiments of the present invention model differentdeployment options and node placements and factor that information inthe analysis of the data received from the nodes. Therefore, in certainembodiments, the analysis models may give different weightage todifferent nodes (or sensor arrays) based on the location, type, and ordensity of nodes in a monitored area. For example, if an area has alarge number of first type sensor nodes, a single node indicating thepresence of a particular agent when the other nodes do not indicate thepresence of such an agent is given less weightage than if the nodeindicating the agent was in an area with relatively sparse coverage ofnodes.

In certain embodiments, the second type sensors (or more sensitivesensors) may be provided with preconcentrators. Such preconcentratorsare used for improved performance with analytical equipment such as gaschromatographs and mass spectrometers. More recently, miniaturizedversions of these devices have been developed for use with hand helddevices. While such a device does offer the possibility of sensitivityand perhaps even specificity enhancements, it does come with a price ofadditional power needs, reduced system robustness, increased operationalcosts, and more complex manufacturing. Therefore, this capability maynot be used on all nodes and a tradeoff of incorporation of thepreconcentrator is made before deciding how many of the nodes wouldinclude a preconcentrator.

FIG. 13 shows a micromachined preconcentrator CASPAR 1301 (CascadeAvalanche Sorbent Plate ARray), which can be used to selectively trapanalyte(s) of interest and thermally desorb a narrow time width pulse ofconcentrated analyte into a narrow orifice intake. The design of CASPARprovides a high surface area “collection plate” with an extremelylow-pressure drop, to allow a high flow to be passed through the deviceand intimately contact the majority of the collection surface, with theminimum power expended. Collection flow is directed normal and directlythrough the surface of CASPAR, which is machined with a dense array ofholes or perforations. Approximately 50% of the surface corresponds toair openings. One or more collection plates can be used as necessary.Multiple plates can also be stacked to provide increased collectionefficiency, however a single collection plate has been demonstrated asan efficient analyte collector design for explosives and a nerve agentsimulant (DMMP).

Alternative micromachined preconcentrator technologies have beendeveloped in which air collection flows are directed parallel to thecollection surface. This approach does not allow high airflows, withintimate air to collector surface contact.

The surface of CASPAR is coated with one or more areas of sorbentpolymer(s), which act to selectively collect and concentrate analyte atambient temperatures. The sorbent polymers for a number of analytesincluding chemical agents have been designed for trapping chemicalagents. These materials have also been specifically designed with hightemperature stabilities, necessary for thermal cycling. Naval ResearchLaboratories (NRL) “HC” polymer coated CASPAR devices have beendemonstrated to provide very high collection efficiencies for the nerveagent, dimethylmethylphosphonate (DMMP). Even with an “early”non-optimized prototype device, sensitivity gains observed were in theregion of multiple orders of magnitude. After thousands of thermaldesorption cycles, no degradation in device performance has beenobserved. Multiple areas of CASPAR coated with different sorbentmaterials, targeting different agents and TICS, can be thermallydesorbed in sequence and from initially different operating temperaturesto different desorbing temperatures to provide additional measures ofanalyte selectivity.

The low thermal mass of CASPAR allows the device to be heated fromambient to analyte desorption temperatures in the milliseconds timedomain. This allows the injection of a high concentration analyte sampleinto the sensor module. CASPAR can be thermally ramped to intermediarytemperatures to allow desorption of analytes that correspond todifferent vapor pressures as shown in the diagram 1401 in FIG. 14. Thisprocess offers separation between more volatile analytes such ashydrocarbon fuels, other solvents and analytes of interest such as thechemical agents. In addition, multiple areas of CASPAR coated withdifferent sorbent polymers, targeting different analytes, can bethermally desorbed in sequence to provide additional measures of analyteselectivity. Flow through CASPAR will be provided by a miniature fanduring collection and a miniature pump during desorption.

Some of the technology discussed herein are described in greater detailin the following U.S. patents, whose entire disclosures are incorporatedherein in their entireties:

U.S. Pat. No. 6,234,006 Hand held sensing apparatus

U.S. Pat. No. 6,085,576 Hand held sensing apparatus

U.S. Pat. No. 6,418,783 Hand held sensing apparatus

U.S. Pat. No. 6,537,498 Colloidal particles used in sensing arrays

The invention is described herein with reference to accompanyingdrawings. These drawings illustrate certain details of specificembodiments that implement the systems and methods and programs of thepresent invention. However, describing the invention with drawingsshould not be construed as imposing on the invention any limitationsthat may be present in the drawings. The present invention contemplatesmethods, systems and program products on any computer readable media foraccomplishing its operations. The embodiments of the present inventionmay be implemented using an existing computer processor, or by a specialpurpose computer processor incorporated for this or another purpose.

As noted above, embodiments within the scope of the present inventioninclude program products on computer-readable media and carriers forcarrying or having computer-executable instructions or data structuresstored thereon. Such computer-readable media can be any available mediawhich can be accessed by a general purpose or special purpose computer.By way of example, such computer-readable media can comprise RAM, ROM,EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to carry or store desired program code in the form ofcomputer-executable instructions or data structures and which can beaccessed by a general purpose or special purpose computer. Wheninformation is transferred or provided over a network or anothercommunications connection (either hardwired, wireless, or a combinationof hardwired or wireless) to a computer, the computer properly views theconnection as a computer-readable medium. Thus, any such a connection isproperly termed a computer-readable medium. Combinations of the aboveshould also be included within the scope of computer-readable media.Computer-executable instructions comprise, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions.

The invention has been described in the general context of method stepsor system components which may be implemented in one embodiment by aprogram product including computer-executable instructions, such asprogram modules, executed by computers in networked environments.Generally, program modules include routines, programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of program code for executing steps of the methods disclosedherein. The particular sequence of such executable instructions orassociated data structures represent examples of corresponding acts forimplementing the functions described in such steps.

The present invention is suitable for being operated in a networkedenvironment using logical connections to one or more remote computershaving processors. Logical connections may include a local area network(LAN) and a wide area network (WAN) that are presented here by way ofexample and not limitation. Such networking environments are commonplacein office-wide or enterprise-wide computer networks, intranets and theInternet. Those skilled in the art will appreciate that such networkcomputing environments will typically encompass many types of computersystem configurations, including personal computers, hand-held devices,multi-processor systems, microprocessor-based or programmable consumerelectronics, network PCs, minicomputers, mainframe computers, and thelike. The invention may also be practiced in distributed computingenvironments where tasks are performed by local and remote processingdevices that are linked (either by hardwired links, wireless links, orby a combination of hardwired or wireless links) through acommunications network. In a distributed computing environment, programmodules may be located in both local and remote memory storage devices.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification and the practice ofthe invention disclosed herein. It is intended that the specification beconsidered as exemplary only, with the true scope and spirit of theinvention also being indicated by the following claims and equivalentsthereof.

1. A method of monitoring for chemical or other toxic agents,comprising: operating a plurality of first type sensors having a firstlevel of sensitivity to an agent in a monitored area; concurrentlyoperating a second type sensor having a second level of sensitivity tothe agent in the monitored area, wherein the second level of sensitivityis at least ten times more sensitive than the first level ofsensitivity; and receiving and analyzing, at a central location, inputfrom the plurality of first type sensors and the second type sensor inorder to determine the presence of the agent in the monitored area. 2.The method according to claim 1, wherein the second level of sensitivityis at least one hundred times more sensitive than the first level ofsensitivity.
 3. The method according to claim 1, wherein both theplurality of first type sensors and the second type sensor are operatedcontinuously.
 4. The method according to claim 1, wherein both the firsttype sensors and the second type sensors comprise chemiresistor basedsensor arrays
 5. The method according to claim 4, wherein thechemiresistor based sensor arrays comprise conductive polymer compositevapor sensors.
 6. The method according to claim 4, wherein thechemiresistor sensor arrays comprise orthogonal sensing technologies ona single sensor array.
 7. The method according to claim 1, furthercomprising providing a preconcentrator with the second type sensor. 8.The method according to claim 1, wherein the agents comprise one or morefrom the group consisting of chemical warfare agents and toxicindustrial chemicals.
 9. The method according to claim 1, wherein thefirst level of sensitivity is the IDLH (Immediately Dangerous to Life orHealth) level and the second level of sensitivity is the PEL(Permissible Exposure Level) level.
 10. The method according to claim 1,further comprising activating an alarm only when data analyzed from botha first type sensor and the second type sensor indicate presence of aparticular agent.
 11. The method according to claim 1, furthercomprising activating an alarm only when two separate analytical modelsapplied to data from either a first type sensor or a second type sensorindicate the presence of a particular agent.
 12. The method according toclaim 11, wherein the analytical model includes assigning differentweights to different sensors based on the type or location of the sensoror the density of sensors at a location.
 13. The method according toclaim 11, wherein activating the alarm is determined based on a modelconfigured such that the results from the two separate analytical modelsindicate a false alarm percentage of less than 0.01% and the falsepositive percentage of less than 5% for all agents tested at the IDLHlevel of concentration.
 14. The method according to claim 1, furthercomprising: determining an optimum layout and number of first and secondtype sensors in the monitored area by modeling to meet specifiedperformance standards and minimizing costs.
 15. A system for monitoringfor chemical or other toxic agents, comprising: a plurality of firsttype sensors, having a first level of sensitivity to an agent, arrangedin a monitored area; a second type sensor, having a second level ofsensitivity to the agent, arranged in the monitored area, wherein thesecond type of sensor is configured to operate concurrently with theplurality of first type sensors, wherein the second level of sensitivityis at least ten times more sensitive than the first level ofsensitivity, and a central analysis unit connected to the plurality offirst type sensors and the second type sensor, wherein the centralanalysis unit analyzes data from the plurality of first type sensors andthe second type sensor in order to determine the presence of the agentin the monitored area.
 16. The system according to claim 15, wherein thefirst type sensors and the second type sensors comprise chemiresistorbased sensor arrays.
 17. The system according to claim 16, wherein thechemiresistor based sensor arrays comprise conductive polymer basedvapor sensors.
 18. The system according to claim 15, wherein the secondtype sensor further comprises a preconcentrator.
 19. The systemaccording to claim 15, wherein the central analysis unit is configuredto activate an alarm only when input from both a first type sensor andthe second type sensor indicate the presence of a particular agent. 20.The system according to claim 15, wherein the central analysis unit isconfigured to activate an alarm only when two separate analytical modelseach indicate the presence of a particular agent when provided withinput from either a first type sensor or a second type sensor.